Envelope Filters

Envelope filters combine two separate electronic processes. First is the “envelope follower,” the portion of the circuit that produces a “control voltage” (CV) in proportion to the volume of the input signal. Think of a VU meter’s bouncing needle. It moves toward the red-zone as the audio signal’s volume increases. Imagine that this needle is tracking a voltage. An envelope follower simply reflects the input’s volume, tracking the dynamics of a musical performance. The envelope follower may respond instantaneously or slowly to changes in a bass’s volume. Its relationship to the input signal can be lockstep tight or loose. These variables are inherent to the sonic variety of effects that incorporate envelope followers. Envelope filters often include control over sensitivity, governing the amount of signal necessary to trigger the envelope follower.
In an envelope filter pedal, an envelope follower is teamed with a lowpass filter, a simple circuit that cuts high frequencies above a certain cutoff point. As this cutoff frequency shifts across the spectrum, we hear the tone color of an audio signal change. When the cutoff frequency is emphasized, we hear this shift even more dramatically. An envelope filter uses the envelope follower’s CV output to slide the cutoff frequency across the frequency spectrum. Filter pedals often include a “resonance” or “peak” control that controls the gain of the signal just below the cutoff frequency, increasing the audibility of the shifting-frequency effect. The cutoff frequency can either start low in the signal’s spectrum and shift higher as the input signal volume increases, or it can start high and move lower. This is the “up” or “down” setting of some envelope filters.

Ashdown Bass Envelope Filter

For those who admire Ashdown’s reputation for stylish-looking products, its bass effects won’t disappoint. I loved the Bass Envelope Filter’s silver-on-purple chassis, nifty VU meter, and rack-style rails, but I’m no fan of the stick-on footpads, one of which quickly disappeared from the bottom. The shiny instrument-style knobs look chic, too, but they’re a tad close together for finger facility, and it’s odd that some control two-position choices, like up/down and bandpass/lowpass, where a rocker-switch would normally do. It’s not just style, though: The purple pedal pours out deep, syrupy-sweet analog filter sounds, with the input level knob effectively serving as sensitivity control. In both up and down mode, the pedal has a slow to medium response for some deliciously liquid sounds. I loved it, but having a filter that closes slowly means a second note will likely lack the quack-attack, remaining in the murky darkness. True-bypass and an output control are terrific touches, too.

List $135
Street $100
Power 9V batt. or AC adapter
True bypass Yes
Weight 2 lbs, 11 oz
Warranty One year limited
Made in China
Contact (718) 937-8300; www.ashdownmusic.com

Boss AW-3 Dynamic Wah

The venerable Boss compact pedal has a rugged aluminum chassis, rubber-padded bottom, side jacks, thumbscrew battery compartment, and rear power jack—features that add up to problem-free pedalboard or stage use. The AW-3 Dynamic Wah adds a bass input and bypass out to the standard Boss feature set. In its up, down, and sharp modes, the AW-3 produces perfectly trippy bwaps and dyoops with good decay and filter control. The digital flavor sometimes feels a tad too perfect—there’s hardly a hint of analog warble—and the filter sometimes closes a bit sharply. However, those digi-guts mean multiple modes for bonus sounds and max buck-bang. The humanizer lets you choose a pair of vowels—yeah, we’re talking phonics—like eee-ooo or aah-ohh, that your notes will mimic. You can also make the filter oscillate for a constant wahwahwah, using the pedal to tap in your wahwah tempo. Dynamic indeed.

List $179
Street $99
Power 9V batt. or AC adapter
True bypass No
Weight 15 oz w/battery
Warranty Five years parts, 90 days labor
Made in Taiwan
Contact (323) 890-3700; www.bossus.com

Chunk Systems Agent 00Funk Mark II

Dressed fly in purple with mission-ready components and stylish yellow labels, Agent “Double-O” Funk is licensed to thrill in her majesty’s secret groove service. The Agent is armed with super-sick sounds—up mode is especially scrumptious—but finding your sonic way can be an adventure. You’ll need to work up to the required clearance level before understanding how the four oddly named knobs interact. Pretending squelch is called “peak” and sweep is labeled “sensitivity” will get you part way. The pots’ performance ranges are wide, so expect ultra-deep lows, crazy highs, and even sharp pops of note-attack signal distortion. Down also has trippy sounds, but it has a noisy hiss, and at several settings notes bottomed out, disappearing entirely while the filter was fully opened. The envelope out jack links the pedal with Chunk’s Brown Dog (see page 44) for mega-weirdness. The 00Funk has amazing analog sounds, but sometimes notes just an octave apart behave completely differently, so plan on searching for that setting sweet-spot.

List $290
Street $230
Power 9V batt. or AC adapter
True bypass Yes
Weight 2 lbs
Warranty Three years limited
Made in Australia
Contact Dist in the U.S. by Godlyke, (973) 777-7477; www.chunksystems.com

Danelectro French Fries Auto Wah

It’s purple. It’s cute. It’s cheap. But despite its Pokémon-like appeal and deep-fried name, the Danelectro French Fries has a decidedly low-cal sound. Aside from the lo or hi range toggle switch, there’s just one thing to tweak: a frighteningly flimsy-feeling resonance knob—which actually seems to be a manual cutoff control. Fortunately, a frosty, art-deco-esque plastic guard protects both knob and toggle. Your best bass bet is to set range to lo and keep resonance at noon or lower. You’ll maintain most of your bypassed bottom, and you’ll gain a little filter-sweep flavor dancing across the highs and mids. Crank resonance too far and you’ll realize we’re talking thin-cut spuds, not steak fries or even crinkle-cuts. Switching range to hi is an express train to thin city. While initially the Fries didn’t seem to be worth its salt, I admit I kept going back for more; there was something compelling about its slender sweeps and bubble-pop attacks. And maybe that’s enough. After all, you wouldn’t expect a $40 stompbox to “ketchup” to the boutique pedals.

List $49
Street $35
Power 9V batt. or AC adapter
True bypass No
Weight 12 oz
Warranty One year limited
Made in China
Contact www.danelectro.com

Digitech Bass Synth Wah

The Bass Synth Wah uses DigiTech’s Audio DNA processor to produce a relatively large number of sounds for relatively few dollars. The rugged metal pedal has a great green-sparkle look and stage-gripping rubber pad, but the knobs feel flyweight. Changing the battery requires tools like the tip of two instrument cables to mash in the spring hinges and remove the footpedal, but with the footpedal off you could easily knock out the rubber rectangle that clicks the effect on. The pedal’s first mode is an upward-moving envelope filter with good sensitivity and an almost analog-like sound. The second blends a low octave with the filter—a nice combo. The last five modes are nasty-sounding synths, and not good-nasty. One self-oscillated to randomly play extra notes—kind of an auto-clam function. Other sounds seemed more about impressing on the sales floor than using onstage. But the first two modes are worth the price, plus you get weird-sounding extras. And one player’s bad-nasty is another’s good-nasty.

List $119
Street $80
Power 9V batt. or AC adapter
True bypass No
Weight 1 lb, 6 oz
Warranty One year, or five years in U.S. with online registration
Made in China
Contact 800-777-3637; www.digitech.com

EBS Bassiq

The compact BassIQ has a high-end price and superb construction to match. It looks and feels super tough, with rounded corners, a rubber-padded bottom, recessed knobs, and a stylish paint job. A tiny mode-switching toggle sits safely between the knobs, with all three settings getting warm, slippery sounds with oodles of sensitivity. Threshold works like a sensitivity control, making the pedal quack or dyoop differently as you vary your attack. Turning down attack opens the filter with a sharper attack and closes it with a quicker decay, while goosing it even a little produces a longer, more languorous glurp. Hi-q spices the up mode’s rising quack with increased resonance for a more pronounced effect. The down mode is especially groovy, diving quick but oh-so-deep with threshold set high and attack set fairly low. It’s the pedal’s touch sensitivity, though, that provides full-filter fun factor.

List $249
Street $200
Power 9V batt. or AC adapter
True bypass No
Weight 1 lb
Warranty Two years limited
Made in Sweden
Contact Dist. in the U.S. by Brooklyn Gear, (718) 858-4900; www.ebssweden.com

Electro-Harmonix Micro Q-Tron

Electro-Harmonix has an entire love-in of filter-rific ’70s-style envelope pedals, but the company chose to send us the newest: the Micro Q-Tron. Much smaller than its stage-hogging, sheet-metal siblings, the sturdy aluminum Micro has a raw look and groovy graphics. The knobs looked plain and felt cheap, battery changes required removing four screws, and the mode switch’s three positions functioned backward: hp was a lowpass filter, and vice-versa. (E-H’s Rick Stevenson says this was a first-run printing goof, not an engineering error.) I consider E-H’s Q-Tron and Mini Q-Tron old friends, but the Micro disappointed me. In lowpass mode, the filter range was relatively high, meaning unaffected lows came through strongly but with a too-subtle effect. I was never able to dial up super-sharp peaks or deeply drippy falls. Bandpass mode had more range, but that’s more useful on guitar. For bass, you’ll be more satisfied with the Micro Q-Tron if you consider it more of a seasoning than a main course.

List $110
Street $83
Power 9V batt. or AC adapter
True bypass Yes
Weight 12 oz
Warranty One year limited
Made in U.S.A.
Contact (718) 937-8300; www.ehx.com

Emma DB-1 Discumbobulator

The Discumbobulator comes from Denmark, where days are long and pedals are funky. It’s honey-mustard color and gentle amber LED look niftier than you’d expect from such a simple design and rugged build. The full-bottom rubber pad and ultra-sturdy knobs portend a long life of stage use. EMMA’s aim was a pedal that could track very quickly, which it accomplishes both in the slurp-o-licious up mode and deep-diving down mode. The knobs behave predictably, but it’s hard to get a broad range of sounds with bass. In particular, the width control has little effect unless you turn it up pretty far. In up mode, the sens knob has a wide-ranging impact on how long the filter is open; with a medium-output active bass, I found a 3 to 6 o’clock sweet spot for funky bass quacks. With all three knobs full up, the down effect has a nice, sharp falling sound that’s not too dark. Overall, the DiscumBOBulator has an open, trebly sound.

List $260
Street $195
Power 9V batt. or AC adapter
True bypass Yes
Weight 1 lb
Warranty Three years limited
Made in Denmark
Contact Dist. in the U.S. by Godlyke; (973) 777-7477; www.godlyke.com

Haz Labs Mu-Tron III+

HAZ Labs’ Mu-Tron III+ is a faithful reproduction of the original ’70s Musitronics Mu-Tron III envelope filter, with upgraded components. That faithfulness carries through some weird stuff: The jacks are reversed from most pedals, which, together with its immodest size, makes the III+ a pedalboard pest. There’s no effect-on indicator (the light helps set filter peak or indicates low battery), so you’d better remember whether you turned it off between the funk jam and the ballad. Worst of all, there’s an on/off switch right up front that loudly kills your signal—yikes! Oh, but then there’s the tone. Brimming with juicy, analog slurps, swoops, and quacks—à la Bootzilla—the Mu-Tron III+ has all the sonic options: up or down movement, band selection, and low or high filter sweep. If that’s not enough, dip switches in the battery compartment affect specific performance changes. Deliciously sensitive and warm, the III+ is a tub of buttery fun.

List $299
Street $225–$250
Power source Two 9V batts. or 24-volt AC adapter
True bypass Yes
Weight 3 lbs, 4 oz
Warranty Two years limited
Made in U.S.A.
Contact (908) 453-3300; www.mu-tron.com

Ibanez AW7 Autowah

Something that sounds as wild as the Ibanez AW7 shouldn’t look so drab and utilitarian. Looks aside, I have no construction complaints about this funky little filter with optional distortion. It has a rugged rubber bottom pad, knobs that depress to stay set and out of the way, and a nifty latch-button for popping open the battery compartment. The type switch selects between lpf or wah, comparable to other pedals’ lowpass and bandpass, and both modes offer groovy gravy for bass, with huge, bottomy lows in lpf mode and solid fundamental in wah. Though it may at times be a bit too perfect and predictable for analog fans, the AW7 is a great-sounding filter with righteous sensitivity control. My favorite sound—which I achieved with no other pedal—had sens near noon and manual off for big, round bwomps that opened and closed almost like a gate. You can place the optional distortion before or after the wah, for different levels of gritty skronk.

List $99
Street $59
Power 9V batt. or AC adapter
True bypass No
Weight 1 lb
Warranty One year limited
Made in China
Contact www.ibanez.com

Maxon AF-9 Auto Filter

I tend to get clumsier around expensive, delicate things, so I was concerned about the fate of the Maxon AF-9’s lightweight plastic-covered sliders and switches. My fears were assuaged after I saw how I interacted with the controls, heard what the pedal could do, and took note of the three-year warranty. The sliders-and-switches setup made for particularly intuitive interaction, especially considering how most envelope filters have at least a knob or three of somewhat arcane function. The AF-9 does all the classic moves—up and down modes, hi and low effect ranges, and bandwidth selection—but having peak and sens on sliders is what seems to make all the difference. The pedal’s watery glurble captures the classic Mu-Tron sound, and it can be extraordinarily sensitive over the full range, especially for finding that finger-pressure sweet spot. Dubwise bonus: Turn sens all the way off for the deepest, darkest reggae sound ever.

List $250
Street $190
Power 9V batt. or AC adapter
True bypass Yes
Weight 1 lb, 8 oz
Warranty Three years limited
Made in Japan
Contact Dist. in U.S. by Godlyke, (973) 777-7477; www.maxonfx.com

Moog Moogerfooger Lowpass Filter

The Moogerfooger Lowpass Filter’s wood side-panels may evoke ’70s station wagons, but the sounds are Magic Bus. Fortunately its components are Maserati, since there are lots to fiddle with. The knobs cover an expansive range, which, for bass, is good and bad: It’s less easy to get classic envelope sounds—it lacks a down mode entirely—but it does everything quite well, including wild stuff. I liked starting with the succulent glorps that came from keeping resonance around 7 or 8, and setting cutoff in a quarter-turn range centered around 250Hz. From there, amount gave me a bright-to-dark color range and luscious finger sensitivity. Blending in a dry signal with the mix knob did more than preserve the fundamental; the unaffected bass had its own trippy interaction with the filter glurps. With an expression pedal or another pedal’s envelope-out signal, the back-panel patch bay jacks give even more control over the sonic sauce.

List $279
Street $265
Power source AC adapter
True bypass No
Weight 2 lbs, 5 oz
Warranty One year limited
Made in U.S.A.
Contact (828) 251-0090, www.moogmusic.com

MXR Bass Auto Q

Six knobs may seem like a lot, but the MXR Bass Auto Q can do something other filter pedals can’t: provide a shimmering oscillator effect you can blend with the envelope filter. The ultra-sturdy rubber-capped pots smartly outline your boot sole for protection, and just north of the footswitch, an LED both indicates bypass status and gently pulses to reflect the oscillator rate. The first two knobs, which set the filter sweep range and resonance peak, or “q,” control the sound of both the initial filter and trailing oscillator. My favorite setting had range at noon and “q” around 2 o’clock, but even the lowest range setting had abundant bass fundamental. Blend mixes the filter and oscillator; when blend is fully to the left, the oscillator is off and decay controls the filter length. With blend in the middle, decay controls how quickly the oscillator’s wahwahwah follows the filter’s bwap. The Bass Auto Q’s sounds aren’t the wildest, but with plenty of bottom always present, they might be the most consistently useful.

List $229
Street $120
Power 9V batt. or AC adapter
True bypass Yes
Weight 1 lb, 8 oz
Warranty One year limited
Made in U.S.A.
Contact www.jimdunlop.com